Device for protection from thunder

ABSTRACT

This invention aims at preventing a thunderbolt attack detecting circuit from determining that no thunderbolt is approaching because the thunderbolt attack detecting circuit turns to its initial condition due to power interruption caused by an approaching thunderbolt and is changed over into a normal condition in the thunderbolt approaching status maintained. This thunderbolt disaster protecting apparatus comprises a thunderbolt attack detecting circuit for determining whether or not any thunderbolt is approaching by detecting a thunderbolt signal and a switching mechanism for changing over to the normal condition in which a protection object device is connected to an electric path or to thunderbolt resisting condition in which the protection object device is separated from the electric path. And this apparatus obtains a control power supply from the electric path and is changed over to the normal condition at the normal time when no thunderbolt is approaching and to the thunderbolt resisting condition when any thunderbolt is approaching according to a signal from the thunderbolt attack detecting circuit. And when the control power is interrupted, after the control power is restored, this apparatus determines whether or not any thunderbolt is approaching in a predetermined time interval and changes over the status to thunderbolt resisting condition when any thunderbolt is approaching and to the normal condition when the condition is normal.

TECHNICAL FIELD

The present invention relates to a thunderbolt disaster protectingapparatus for protecting an electronic apparatus from being damaged bylightning surge generated accompanied by a thunderbolt, which entersfrom commercial frequency power lines. More particularly, the presentinvention relates to a thunderbolt disaster protecting apparatus whichminimizes power loss accompanied by protecting from a thunder.

TECHNICAL FIELD

Usually; the commercial frequency power path is distributed to buildingsof homes and the like after the voltage of a high voltage line isdropped to 100 V with a pole transformer, supplying electric power toelectric appliances such as refrigerator, washing device, airconditioner and other electric appliances connect to an electric pathand such as TV, telephone, facsimile, personal computer to communicationline.

As regards the electric path and communication line, it has been wellknown that lightning surge is generated due to a thunderbolt on a highvoltage line and that surge is propagated through the electric path andinvades into the buildings thereby damaging electric appliancesconnected to these lines. To protect these electric appliances, athunderbolt disaster protecting apparatus for shutting down supply ofpower while indicating an alarm of thunderbolt by detecting an abnormalvoltage caused by lightning surge and then transmitting a control signalhas been proposed {see, for example, Japanese Patent ApplicationLaid-Open No. HEI5-326108 (pages 2, 3, FIG. 1)}. Further, a thunderboltdisaster protecting apparatus in which a thunderbolt resistanttransformer is inserted into a power line in order to prevent thelightning surge from reaching any electric appliance has been alsoproposed (see, for example, Japanese Patent Application Laid-Open No.HEI03-086017).

However, a circuit for detecting an attack of thunderbolt obtains itspower supply from a household line. However, because the apparatusreturns to its initial state due to power interruption if the householdline is interrupted by the thunderbolt, there is such a problem thatwhen the control power supply is restored again, it is in a state inwhich no thunderbolt is approaching due to the initialization even ifanother thunderbolt is approaching.

Further, if power interruption occurs with the thunderbolt approachingstatus maintained, there is another problem that even if no thunderboltapproaches after the power supply is restored, the thunderboltapproaching state is maintained.

Although as a countermeasure which should be taken when the controlpower supply is interrupted, it can be considered to provide with abackup power supply circuit for memorizing whether the thunderbolt isapproaching using a battery or the like, in this case, there is anotherproblem that the maintenance of the backup power supply is needed.

Further, because in the thunderbolt disaster protecting apparatus usedin the thunderbolt resisting transformer, its power loss due to ironloss of the thunderbolt resisting transformer is as large as 3-10% itstransformer capacity, a thunderbolt resisting means whose power loss issmaller has been demanded.

DISCLOSURE OF THE INVENTION

The present invention is constituted as follows.

-   1. A thunderbolt disaster protecting apparatus comprising a    thunderbolt attack detecting circuit for determining whether or not    any thunderbolt is approaching by detecting a thunderbolt signal,    and a switching mechanism for changing over to a normal condition in    which a protection object device is connected to an electric path or    a thunderbolt resisting condition in which the protection object    device is separated from the electric path, wherein the thunderbolt    attack detecting circuit and the switching mechanism obtain a    control power from the electric path and the thunderbolt attack    detecting circuit changes over the switching mechanism to the normal    condition at the time of normal condition and when any thunderbolt    is approaching, changes over the switching mechanism to the    thunderbolt resisting condition.-   2. The thunderbolt disaster protecting apparatus according to claim    1, wherein the thunderbolt attack detecting circuit further    comprises a power interruption restoration circuit which after the    control power supply is interrupted and then the power interruption    is restored, determines whether or not any thunderbolt is    approaching in a predetermined time interval and changes over the    switching mechanism to the thunderbolt resisting condition if a    thunderbolt is approaching and to the normal condition if the    condition is normal.-   3. A thunderbolt disaster protecting apparatus comprising a    thunderbolt resisting transformer, a thunderbolt attack detecting    circuit for determining whether or not any thunderbolt is    approaching by detecting a thunderbolt signal, and a switching    mechanism for changing over to the normal condition in which a    protection object device is connected to an electric path or to the    thunderbolt resisting condition in which the protection object    device is connected to the electric path through the thunderbolt    resisting transformer, wherein the thunderbolt attack detecting    circuit and the switching mechanism obtain a control power from the    electric path and the thunderbolt attack detecting circuit changes    over the switching mechanism to the normal condition at the time of    normal condition and when any thunderbolt is approaching, changes    over the switching mechanism to the thunderbolt resisting condition.-   4. The thunderbolt disaster protecting apparatus according to claim    3, wherein the thunderbolt attack detecting circuit further    comprises a power interruption restoration circuit which after the    control power supply is interrupted and then the power interruption    is restored, determines whether or not any thunderbolt is    approaching in a predetermined time interval and changes over the    switching mechanism to the thunderbolt resisting condition if a    thunderbolt is approaching and to the normal condition if the    condition is normal.

EFFECT OF THE INVENTION

Because according to the thunderbolt attack protecting apparatus of thefirst invention, only in a period in which a device needs to beprotected from lightning surge due to falling of thunderbolt, theelectric path is shut down and if the forerunning phenomenon of thelightning surge diminishes, the electric path is connected again, it canprotect the device when any thunderbolt is approaching and when thecondition returns to normal one, it can be automatically restored.

When supply of electricity from a control power supply of thethunderbolt disaster protecting apparatus is stopped by powerinterruption due to falling of thunderbolt or the like, even if a backuppower supply for securing the operation at the time of the powerinterruption is not provided, the thunderbolt attack detecting circuitturns into initial condition because of the power interruption when thethunderbolt is approaching. As a result, it is possible to preventeasily the thunderbolt attack detecting circuit form determining that nothunderbolt is approaching and then changing over to the normalcondition, so that any thunderbolt disaster on a protection objectdevice due to the power interruption can be prevented.

When power interruption occurs in the thunderbolt resisting conditionand no thunderbolt is approaching after the power supply is restored,the thunderbolt attack detecting circuit turns into the initialcondition due to the power interruption, so that it is possible toprevent a case in which it is determined that no thunderbolt isapproaching and thus no signal is sent to the operation control means,maintaining the thunderbolt resisting condition.

Further, by determining whether or not any thunderbolt is approaching ina predetermined time interval after power is restored, it is possible torecognize whether or not the thunderbolt is approaching just after thepower is restored. As a result, misjudgment due to initialization of thethunderbolt disaster protecting apparatus can be prevented so as toprotect the protection object apparatus from a damage by thethunderbolt.

According to the thunderbolt attack protecting apparatus of the thirdinvention, by using the thunderbolt resisting transformer, lightningsurge invading from the power supply side is prevented from beingpropagated to the load side by means of the thunderbolt resistingtransformer in addition to the above-described effect, so that theprotection object device can be protected from thunderbolt disaster withthe protection object device being supplied with electricity, withoutinterrupting power to the protection object device even in thethunderbolt resisting condition. At the same time, power consumption dueto iron loss in the thunderbolt resisting transformer at the normal timecan be eliminated.

Further a relatively small thunderbolt resisting transformer can be usedbecause the apparatus does not need to be activated except in a shorttime when any thunderbolt is approaching.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory diagram showing a normal condition of the firstembodiment of the present invention;

FIG. 2 is an explanatory diagram showing the thunderbolt resistingcondition of the first embodiment of the present invention;

FIG. 3 is an explanatory diagram showing the normal condition of thesecond embodiment of the present invention;

FIG. 4 is an explanatory diagram showing the thunderbolt resistingcondition of the second embodiment of the present invention; and

FIG. 5 is an explanatory diagram showing the third embodiment of thepresent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the thunderbolt disaster protecting apparatus of thepresent invention will be described with reference to FIGS. 1-5.

1. EMBODIMENT 1

The first embodiment concerns a thunderbolt disaster protectingapparatus which is connected to a low voltage power line and interruptsa load from the household electric line only during a period in whichthe thunderbolt is approaching, so that no trouble occurs in restorationeven if power interruption happens.

(1) Structure of the Thunderbolt Disaster Protecting Apparatus

The thunderbolt disaster protecting apparatus of the first embodiment isinserted in between an electric path 10 connected to a lead-in wire orthe like introduced from outdoor into a house and a load side electricpath 20 connected to the power supply of a protection object device.

The thunderbolt disaster protecting apparatus 1 comprises a power supplycircuit 4, a thunderbolt attack detecting circuit 5, an operationcontrol means 6 and a status change-over switch 7. Further, in the path10 and the load side path 20, lightning arresting devices 90 eachcomposed of an arrestor and a surge absorbing device are connected so asto cross over the respective phases.

A power supply circuit 4 is connected to the electric path 10 andsupplies electricity obtained from the electric path 10 to thethunderbolt attack detecting circuit 5 and the operation control means6.

The thunderbolt attack detecting circuit 5 is a circuit for detecting athunderbolt to determine whether it is approaching and give aninstruction for an operation corresponding to its result to theoperation control means. In the thunderbolt attack detecting circuit 5,arbitrary detecting means is used single or in plural quantities incombination so as to determine whether or not a thunderbolt isapproaching. By combining plural detection signals upon determination,it is possible to prevent misjudgment.

As a means used for determining whether the thunderbolt is approaching,lightning surge propagated through lightning, thunder, electric wave,electric field and electric path can be exemplified. For example, if thedetermination is made using lightning and thunder, when the light amountand sound level exceed a predetermined value or a difference indetection time of lightning and thunder having the light amount andsound level exceeding the predetermined value drops below apredetermined value, it can be determined that the thunderbolt isapproaching. Further, when the lightning surge exceeds a predeterminedvoltage value or current value or when the occurrence frequency oflightning surge over the predetermined value exceeds a predeterminedvalue, determining that the thunderbolt is approaching can beexemplified. Further, in case of detection by measuring electrostaticfield, determining that the thunderbolt occurs when a predeterminedstrength is exceeded and that value drop rapidly can be exemplified.

If the thunderbolt attack detecting circuit 5 determines that thethunderbolt is approaching, it sends a change-over signal forthunderbolt resisting condition to the operation control means 6. If thecondition which satisfies the thunderbolt approaching conditiondisappears or the condition which satisfies the thunderbolt approachingcondition while a predetermined time has elapsed, it regards that thethunderbolt approaching condition is released and sends a change-oversignal for the normal condition to the operation control means 6.

Further, the thunderbolt attack detecting circuit 5 is provided with apower interruption restoration circuit which after the control powersupply is interrupted and then the power interruption is restored,determines whether or not the thunderbolt is approaching for apredetermined time and instructs the operation control means 6 to changeover to the thunderbolt resisting condition when any thunderbolt isapproaching or to the normal condition when it is in normal condition.

In the meantime, the thunderbolt attack detecting circuit 5 can continueto send a change-over signal for the thunderbolt resisting condition tothe operation control means 6 during a condition in which thethunderbolt is approaching and can determine that it is in the normalcondition when no change-over signal for the thunderbolt resistingcondition is sent.

The predetermined time is permitted to be selected arbitrarily as longas it is over an interval of the thunderbolt and can be of arbitraryduration over an ordinary thunderbolt interval of about 40 m seconds.Although as this example, 50 m seconds, 100 m seconds, 1 second, 10seconds, 1 minute, 30 minutes and 1 hour and the like can be mentioned,but this is not restricted to any particular one.

The operation control means 6 and the status change-over switch 7 areswitching mechanism. The operation control means 6 is a switchingmechanism for controlling the change-over operation on a contact pointof the status change-over switch 7 from the normal condition shown inFIG. 1 to the thunderbolt resisting condition shown in FIG. 2 accordingto a signal of the thunderbolt approaching status from the thunderboltattack detecting circuit 5. This actuates drive sections such as a motorand magnet and the like of the status change-over switch 7 describedlater, to automatically operate the status change-over switch 7 so thatit connects a protection object device to the electric path 10 when itis in the normal condition and it shuts down the protection objectdevice from the electric path 10 when it is in the thunderbolt resistingcondition.

When the thunderbolt approaching status is released, a signal forreleasing the thunderbolt approaching status is sent from thethunderbolt attack detecting circuit 5 to the operation control means 6so that the status change-over switch 7 is changed over from thethunderbolt resisting condition shown in FIG. 2 to the normal conditionshown in FIG. 1. The operation control means 6 keeps its previouscondition until a signal is sent from the thunderbolt attack detectingcircuit 5.

The status change-over switch 7 is composed of a mechanical contactswitch which changes over a protection object device (not shown)connected to the load side electric path 20 between the normal conditionin which it is connected to the electric path 10 and the thunderboltresisting status in which the protection object device is separated fromthe electric path 10. This is, for example, an automatic switch which isactuated by a drive section such as a motor, magnet and suchelectromagnetic contact device as a ratchet relay, keep relay andcircuit breaker can be exemplified. By using these, a current normalcondition or thunderbolt resisting condition can be maintainedmechanically even in non-voltage condition.

The status change-over switch 7 has voltage withstanding capacity ofabout 30 kV capable of withstanding an excessive voltage of lightningsurge in order to prevent lightning surge from being propagated to aseparated load side electric path 20 when the power supply is shut down.

Further, the status change-over switch is permitted to be of any type ofswitch such as mechanical contact point, semiconductor type, as long asit can be controlled by the operation control means.

(2) Operation of the Thunderbolt Disaster Protecting Apparatus

[1] Normal Condition

In a normal condition in which no thunderbolt approaches, the statuschange-over switch 7 is changed over to the normal side in which aprotection object device connected to the load side electric path 20 isconnected to the electric path 10.

Detection of arrival of the thunderbolt by the thunderbolt attackdetecting circuit 5 is carried out continuously.

[2] Thunderbolt Resisting Condition

If the thunderbolt approaches, lightning surge is detected by thethunderbolt attack detecting circuit 5 and the status change-over switch7 is changed over to the separation side. Consequently, a load isseparated from the electric path 10 and protected from lightning surge.

When a predetermined time elapses after a last lightning surge isdetected, it is returned to the normal condition.

[3] Power Interruption and Power Interruption Restoration Condition

If power interruption occurs for a reason, for example, falling ofthunderbolt so that no electric power necessary for operating thethunderbolt disaster protecting apparatus can be obtained, the statuschange-over switch 7 maintains a status before the power interruption.Thus, even if a power interruption occurs in the thunderbolt resistingcondition, the load can be kept to be isolated from the electric path 10and thus, if lightning surge occurs after the power interruption, it canbe protected.

Further, when the status is restored from the power interruption, thethunderbolt attack detecting circuit 5 detects presence or absence oflightning surge and if it is not detected, the status change-over switch7 is changed over to the normal condition and if it is detected, to thethunderbolt resisting condition. If there is any given status, thatstatus is maintained.

2. SECOND EMBODIMENT

The second embodiment concerns a thunderbolt disaster protectingapparatus, which is connected to a low voltage power line and in which athunderbolt resisting transformer is interposed between the electricpath and load when the thunderbolt approaches, thereby when powerinterruption occurs, producing no obstacle in its restoration.

(1) Structure of Thunderbolt Disaster Protecting Apparatus

In the thunderbolt disaster protecting apparatus of the secondembodiment, as shown in FIGS. 3, 4, in the normal condition, thethunderbolt resisting transformer 30 is separated from the electric pathand electricity is supplied to a protection object device (not shown)connected to the load side electric path 20 through bypass lines 8 fromthe electric path 10.

The thunderbolt disaster protecting apparatus 1 comprises a power supplycircuit 4, a thunderbolt attack detecting circuit 5, an operationcontrol means 6 and a status change-over switch 7. Lightning arrestingdevices 90 comprising an arrestor, a surge absorbing device and the likeare connected to the electric path 10 and the load side electric path 20such that they cross over the respective phases.

FIG. 4 is an explanatory diagram of the thunderbolt resisting conditionwhen the thunderbolt resisting condition is changed over. When thethunderbolt attack detecting circuit 5 determines that the thunderboltis approaching, the operation control means 6 changes over the statuschange-over switch 7 to the thunderbolt resisting condition andelectricity is supplied to a protection object device (not shown)connected to the load side electric path 20 in conditions in which thethunderbolt resisting transformer 30 is inserted in between the electricpath 10 and the load side electric path 20.

Using the thunderbolt resisting transformer 30 enables to blocklightning surge invading from the power supply side from beingpropagated to the load side by means of the thunderbolt resistingtransformer 30 and even when the thunderbolt resisting status ismaintained, supply electricity to the protection object device withoutinterruption power to the protection object device.

Particularly because by using an automatic switch or the like which isactuated by a magnet, the change-over time of the status change-overswitch 7 is set to less than 10 m seconds so that the protection objectdevice can be changed over in substantially no power interruptioncondition, the protection object device can be protected from powerinterruption at the time of the change-over. Further, because at thetime of the normal condition, the thunderbolt resisting transformer 30can be separated from the electric path, there is an effect ofeliminating power consumption by non-load loss such as iron loss of thethunderbolt resisting transformer 30.

In case of a device such as a personal computer, connected to both anelectric path and communication line, by providing both the electricpaths 10, 20 and the communication lines 11, 21 as shown in FIG. 5 withthe status change-over switch 7, the protection object device can beprotected. In the meantime, like reference numerals are attached to thesame components as FIG. 1 and description thereof is omitted.

(2) Operation of the Thunderbolt Disaster Protecting Apparatus

[1] Normal Condition

In the normal condition in which no thunderbolt approaches, the statuschange-over switch 7 is changed over to the bypass line 8 side so thatthe thunderbolt resisting transformer 30 is separated thereby producinga state in which no power is supplied. Thus, no electricity loss isgenerated in the thunderbolt resisting transformer 30.

Further, detection of the arrival of the thunderbolt by means of thethunderbolt attack detecting circuit 5 is continued.

[2] Thunderbolt Resisting Status

When the thunderbolt arrives, lightning surge is detected by thethunderbolt attack detecting circuit 5 and the status change-over switch7 is changed over to the side of the thunderbolt resisting transformer30. Consequently, a load is connected to the electric path 10 throughthe thunderbolt resisting transformer 30 thereby protecting fromlightning surge.

Further, when a predetermined time elapses after a last lightning surgeis detected, it returns to normal condition.

[3] Power Interruption and Power Interruption Restoration Condition

If power interruption occurs due to a reason, for example, falling ofthunderbolt so that electric power necessary for operating thethunderbolt disaster protecting apparatus cannot be obtained, the statuschange-over switch 7 is kept in a status before the power interruption.Consequently, even if power interruption occurs in the thunderboltresisting condition, the load can be kept in such a condition in whichit is connected to the electric path 10 through the thunderboltresisting transformer 30 and even if lightning surge occurs after thepower interruption, it can be protected.

When the status is restored from the power interruption, the thunderboltattack detecting circuit 5 detects the presence or the absence oflightning surge and if it is not detected, the status change-over switch7 is changed over to the normal condition and if it is detected, to thethunderbolt resisting condition. In the meantime, if there is any givencondition, that condition is maintained.

3. THIRD EMBODIMENT

In FIG. 5, a thunderbolt resisting transformer 30 can be inserted inbetween the electric path 10 and the load side electric path 20 when thethunderbolt resisting condition arises, as shown in FIG. 3.Alternatively, it is possible to provide only a communication line 11,21 with the status change-over switch 7 so as to change over between thenormal condition and the thunderbolt resisting condition

Next, the operation of a case where the electric path 10 is interruptedby falling of thunderbolt or the like will be described. Due to thepower interruption, supply of electricity of the thunderbolt disasterprotecting apparatus 1 to the power supply circuit 4 is eliminated,stopping the operation of the thunderbolt attack detecting circuit 5. Inthe meantime, because the status change-over switch 7 is mechanicallymaintained, the normal condition just before power interruption and thethunderbolt resisting condition can be maintained during powerinterruption also.

If an electromagnetic contact device such as a relay which is restoredwithout voltage as the status change-over switch 7 is used, bymemorizing a status just before power interruption into the operationcontrol means 6 using an electric means such as a memory or a mechanicalmeans such as a keep relay, the status just before power interruptioncan be restored easily just after the power is restored.

By memorizing the status just before the power interruption in theoperation control means 6, the status change-over switch 7 on operationcan be operated securely up to a normal position during restoration ofthe power supply.

Then, the thunderbolt attack detecting circuit 5 detects the presence orthe absence of approaching thunderbolt in a predetermined time intervalafter the power is restored. The thunderbolt attack detecting circuit 5instructs the operation control means 6 to turn the status change-overswitch 7, if the thunderbolt is detected once or more in thepredetermined time interval, to be in the thunderbolt resistingcondition and if no approaching thunderbolt is detected, to be in thenormal condition. In the meantime, the aforementioned predetermined timecan be set to arbitrary time between several seconds and several tensminutes.

In this way, the thunderbolt attack detecting circuit 5 detects thepresence or the absence of approaching thunderbolt in a predeterminedtime after the power is restored and based on that result, turns thestatus change-over switch 7. Consequently, the thunderbolt attackdetecting circuit 5 turns into initial condition due to powerinterruption, so that sending of a change-over signal to the operationcontrol means 6 so as to obtain the normal condition by determining thatno thunderbolt approaches can be eliminated. Alternatively, if powerinterruption occurs in the thunderbolt resisting condition and anythunderbolt does not approach after the power is restored, thethunderbolt attack detecting circuit 5 turns into the initial conditiondue to power interruption, so that it is determined that no thunderboltis approaching and then, any signal is not sent to the operation controlmeans 6 thereby preventing the thunderbolt resisting condition frombeing maintained. Further, whether or not the thunderbolt is approachingjust after the power is restored can be recognized thereby blockingmisjudgment.

If any backup power supply for securing the operation during powerinterruption is not provided, the thunderbolt attack detecting circuit 5turns into initial condition due to power interruption when thunderboltapproach is continued and the thunderbolt attack detecting circuit 5determines that no thunderbolt is approaching, thereby preventing thestatus from being changed over to the normal condition. As a result, theprotection object device can be protected from a thunderbolt.Alternatively, by maintaining the thunderbolt resisting condition, thestatus in which supply of electricity to the protection object device isstopped can be eliminated.

If the thunderbolt resisting transformer 30 is used, it is permissibleto turn the circuit into the thunderbolt resisting condition once whenthe power is being restored, and as a result, it is possible to suppressgeneration of any lightning disaster just after the power is restored.

In the meantime, the present invention is not limited to theabove-described embodiments and may be modified in various ways within ascope of the present invention depending on purpose and application.

For example, a thunderbolt attack detecting means for detecting athunderbolt attack as a result of at least one of lightning, thunder,lightning surge, electromagnetic wave and electric field and theswitching mechanism can, after a forerunning phenomenon of thunderboltis not detected or the thunderbolt attack is detected by the thunderboltattack detecting means, change over its switching mechanism switch tothe normal condition temporarily. Even if any thunderbolt attack occurs,by maintaining the thunderbolt resisting condition only during athunderbolt attack period, the thunderbolt resisting transformer canprotect it even if plural thunderbolt attacks (multiple thunderbolts)happen in a single falling of thunderbolt.

The switching mechanism can be changed over to the normal conditionafter a predetermined forerunning period calculated since theaforementioned forerunning phenomenon is detected and a predeterminedlightning period calculated since the thunderbolt attack phenomenon isdetected both elapse. Consequently, since the forerunning phenomenon isout of detection, the status returns to the normal condition after theforerunning period elapses and as a result, the device can be protectedonly in a period in which the thunderbolt may be generated.

There are further provided a manual operation switch and a manualoperation instructing means and the manual operation instructing meansinstructs manual operation or manual operation release to thethunderbolt attack detecting circuit depending on the operation of themanual operation switch. If the manual operation is instructed, thethunderbolt attack detecting circuit changes over the switchingmechanism to the thunderbolt resisting condition and if the manualoperation release is instructed, changes over the switching mechanism tothe normal condition.

When the switching mechanism is changed over to the thunderboltresisting condition, the thunderbolt attack detecting circuit can beinhibited from an operation of changing over to the normal conditioneven if the manual operation release instruction is received, until apredetermined thunderbolt resisting period elapses since when theswitching mechanism is changed over to the thunderbolt resistingcondition and/or when the forerunning phenomenon is detected.

By providing the manual operation switch and the manual operationinstructing means, the thunderbolt resisting condition can be set upmanually, so that protection from lightning surge can be carried outsecurely. Further, by disabling manual release of the thunderboltresisting condition in a period in which the thunderbolt resistingcondition is maintained, a disaster due to erroneous operation can beprevented.

A detection line of lightning surge signal used in the thunderboltattack detecting circuit can be connected to the shield and iron core ofthe thunderbolt resisting transformer. The shield and iron core of thethunderbolt resisting transformer are often grounded and by obtaining alightning surge signal from this grounding line, stray capacitance ofthe thunderbolt resisting transformer is used and this is used as asubstitute of a coupling capacitor for detection. Thus, any expensivecoupling capacitor having a specially high voltage withstanding capacitydoes not need to be used and therefore, this can be produced at cheapcost. Further, because the necessity of the coupling capacitordiminishes at the same time, the thunderbolt resisting transformer isallowed to be of the same size as a conventional one, so that theapparatus can be reduced in size.

Further, there are further provided a first determining means whichdetects a lightning surge signal with the thunderbolt attack detectingcircuit, compares the detection signal of a detected lightning surgewith a predetermined judgment value and if the judgment value is over apredetermined first level value and the lightning surges over apredetermined number occur in a predetermined time, determines that thethunderbolt is approaching and a second determining means in which thejudgment value is set at a predetermined second level value higher thanthe first level value and if lightning surge over the second leveloccurs, determines that the thunderbolt is approaching and if any one ofthe first determining circuit and the second determining circuitdetermines that the thunderbolt is approaching, that the thunderbolt isapproaching can be determined.

By using the first determining means, it is possible to determine thatthe thunderbolt, which approaches from far away gradually, isapproaching without any erroneous judgment and by using the seconddetermining means, it is possible to immediately determine that anythunder cloud developed nearby rapidly approaches. Thus, the protectionobject device can be protected from thunderbolt disaster securely.

1. A thunderbolt disaster protecting apparatus comprising: a thunderboltattack detecting circuit for determining whether or not any thunderboltis approaching by detecting a thunderbolt signal; and a switchingmechanism for changing over to a normal condition in which a protectionobject device is connected to an electric path or a thunderboltresisting condition in which the protection object device is separatedfrom the electric path, wherein said thunderbolt attack detectingcircuit and said switching mechanism obtain a control power supply fromsaid electric path and said thunderbolt attack detecting circuit changesover said switching mechanism to said normal condition at the time ofnormal condition and when any thunderbolt is approaching, changes oversaid switching mechanism to said thunderbolt resisting condition, andsaid thunderbolt disaster protecting apparatus further comprising apower interruption restoration circuit which after said control powersupply is interrupted and then the power interruption is restored,determines whether or not any thunderbolt is approaching in apredetermined time interval and changes over said switching mechanism tosaid thunderbolt resisting condition if a thunderbolt is approaching andto said normal condition if the condition is normal.
 2. The thunderboltdisaster protecting apparatus according to claim 1, wherein saidswitching mechanism can be maintained mechanically the normal conditionor the thunderbolt resisting condition of the time of change-over evenin non-voltage condition.
 3. A thunderbolt disaster protecting apparatuscomprising: a thunderbolt resisting transformer; a thunderbolt attackdetecting circuit for determining whether or not any thunderbolt isapproaching by detecting a thunderbolt signal; and a switching mechanismfor changing over to the normal condition in which a protection objectdevice is connected to an electric path or to the thunderbolt resistingcondition in which said protection object device is connected to theelectric path through said thunderbolt resisting transformer, whereinsaid thunderbolt attack detecting circuit and said switching mechanismobtain a control power from said electric path and said thunderboltattack detecting circuit changes over said switching mechanism to saidnormal condition at the time of normal condition and when anythunderbolt is approaching, changes over said switching mechanism tosaid thunderbolt resisting condition.
 4. The thunderbolt disasterprotecting apparatus according to claim 3, wherein said thunderboltattack detecting circuit further comprises a power interruptionrestoration circuit which after said control power supply is interruptedand then the power interruption is restored, determines whether or notany thunderbolt is approaching in a predetermined time interval andchanges over said switching mechanism to said thunderbolt resistingcondition if a thunderbolt is approaching and to said normal conditionif the condition is normal.